To date we have studied biospecimens from patients with severe chronic periodontitis including oral/gingival tissues, fluids and biofilms and have identified an upregulation of IL-17 related immune responses in periodontitis. Periodontitis lesions were found to be abundantly populated by IL-17 secreting cells, cells linked to infection, chronic inflammation, autoimmunity and pathology. These findings expand previous clinical studies demonstrating high levels of IL-17 cytokine in the sera and tissues of patients with periodontitis. Expression of the signature Th17 cytokine IL-17 as well as the Th17 supporting cytokines IL-1, IL-6 and IL-23 were also significantly higher in diseased lesions and tissue exudates. Finally, expression of IL-17 correlated with increased tissue damage in periodontitis. Our supporting in vitro studies have also demonstrated a role for the periodontal pathogen P. gingivalis in the development of Th17 responses in vitro. We have shown that interaction of P. gingivalis with myeloid antigen presenting cells promotes Th17 differentiation. P. gingivalis stimulated production of cytokines linked to Th17 polarization, and not Th1 related cytokines. Accordingly, when supernatants from myeloid cells stimulated with P. gingivalis were added to PBMC, they supported the differentiation of T cells into Th17 but did not influence Th1 differentiation. How various microbes and their products can shape oral mucosal immunity and inflammatory responses in the oral cavity is of increased interest and will continue to be interogated in our program through clinical assocations and mechanists studies in vitro and in animal models.